Despite being a C++ programmer by trade nowadays, I still mess with Flash rather a lot. So one of the main bits of free web development software I've been using lately is Flashdevelop (www.flashdevelop.org) which is free open source software (Windows only) for creating flash content. If you download the Adobe Flex3 SDK (from Adobe, also free) you can use Flashdevelop to create flash movies in AS3....Beats the hell out of paying through the nose for Flash CS4!
I use Blender (www.blender.org) and Google Sketchup (from Google) for creating 3D models to use in my papervision flash projects.
Inkscape (www.inkscape.org), GIMP (www.gimp.org) and Paint.NET (www.getpaint.net) are my image editors of choice (for photo/gfx editing and texturing). All top quality free open source software...Again, eliminating the need to shell out for Photoshop, Illustrator or Fireworks!
I also use Python (www.python.org) for writing Blender scripts and for general system tools.